Inject Config as dependency for database, routing table, and snapshotter

- Remove old database Config struct and related functions
- Update database.New() to accept config.Config parameter
- Update routingtable.New() to accept config.Config parameter
- Update snapshotter.New() to accept config.Config parameter
- Simplify fx module providers in app.go
- Fix truthiness check for environment variables
- Handle empty state directory gracefully in routing table and snapshotter
- Update all tests to use empty state directory for testing

internal/config/config.go

@@ -0,0 +1,91 @@
+// Package config provides centralized configuration management for RouteWatch
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"time"
+)
+
+const (
+	// AppIdentifier is the reverse domain name identifier for the app
+	AppIdentifier = "berlin.sneak.app.routewatch"
+
+	// dirPermissions for creating directories
+	dirPermissions = 0750 // rwxr-x---
+)
+
+// Config holds configuration for the entire application
+type Config struct {
+	// StateDir is the directory for all application state (database, snapshots)
+	StateDir string
+
+	// MaxRuntime is the maximum runtime (0 = run forever)
+	MaxRuntime time.Duration
+}
+
+// New creates a new Config with default paths based on the OS
+func New() (*Config, error) {
+	stateDir, err := getStateDirectory()
+	if err != nil {
+		return nil, fmt.Errorf("failed to determine state directory: %w", err)
+	}
+
+	return &Config{
+		StateDir:   stateDir,
+		MaxRuntime: 0, // Run forever by default
+	}, nil
+}
+
+// GetStateDir returns the state directory path
+func (c *Config) GetStateDir() string {
+	return c.StateDir
+}
+
+// getStateDirectory returns the appropriate state directory based on the OS
+func getStateDirectory() (string, error) {
+	switch runtime.GOOS {
+	case "darwin":
+		// macOS: ~/Library/Application Support/berlin.sneak.app.routewatch
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return "", err
+		}
+
+		return filepath.Join(home, "Library", "Application Support", AppIdentifier), nil
+
+	case "linux", "freebsd", "openbsd", "netbsd":
+		// Unix-like: /var/lib/berlin.sneak.app.routewatch if root, else XDG_DATA_HOME
+		if os.Geteuid() == 0 {
+			return filepath.Join("/var/lib", AppIdentifier), nil
+		}
+
+		// Check XDG_DATA_HOME first
+		if xdgData := os.Getenv("XDG_DATA_HOME"); xdgData != "" {
+			return filepath.Join(xdgData, AppIdentifier), nil
+		}
+
+		// Fall back to ~/.local/share/berlin.sneak.app.routewatch
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return "", err
+		}
+
+		return filepath.Join(home, ".local", "share", AppIdentifier), nil
+
+	default:
+		return "", fmt.Errorf("unsupported operating system: %s", runtime.GOOS)
+	}
+}
+
+// EnsureDirectories creates all necessary directories if they don't exist
+func (c *Config) EnsureDirectories() error {
+	// Ensure state directory exists
+	if err := os.MkdirAll(c.StateDir, dirPermissions); err != nil {
+		return fmt.Errorf("failed to create state directory: %w", err)
+	}
+
+	return nil
+}